1. Field of the Invention
The present invention relates to a 5-group 8-element zoom lens for projection mountable on a projection-type display apparatus or the like, and to a projection-type display apparatus on which the zoom lens for projection is mounted. In particular, the present invention relates to a zoom lens for projection that magnifies rays of light carrying video information output from a light valve, such as a transmissive or reflective liquid crystal display apparatus and a DMD (digital micromirror device) display apparatus, and projects the magnified rays of light onto a screen. Further, the present invention relates to a projection-type display apparatus on which such a zoom lens for projection is mounted.
2. Description of the Related Art
Projection-type display apparatuses using light valves, such as a liquid crystal display apparatus and a DMD display apparatus, became widely used in recent years. Especially, a projection-type display apparatus using three light valves corresponding to illumination light of RGB primary colors is widely used. The projection-type display apparatus using three light valves modulates the illumination light of three primary colors by the three light valves for respective colors. Further, the modulated light is combined by a prism or the like, and the combined light is projected onto a screen through a projection lens to display an image.
Meanwhile, the sizes of the light valves became small, and the resolutions of the light valves became sharply higher. Further, as personal computers became widely used, a demand for the projection-type display apparatus for use in presentation increased.
Therefore, a projection-type display apparatus having higher performance, a smaller size and a light weight is requested, because such a projection-type display apparatus is conveniently usable, and easily settable. At the same time, a projection lens having a smaller size and a light weight is strongly requested.
As zoom lenses for projection that satisfy such requirements, zoom lenses for projection disclosed, for example, in Japanese Unexamined Patent Publication No. 2004-109896 (Patent Document 1), Japanese Unexamined Patent Publication No. 2004-279958 (Patent Document 2), and Japanese Unexamined Patent Publication No. 2005-156963 (Patent Document 3) are known. The zoom lenses for projection disclosed in Patent Documents 1 through 3 are composed of four or five lens groups, which are seven or eight lenses.
However, in each of the zoom lenses for projection disclosed in Patent Documents 1 through 3, the fourth lens group includes a cemented lens. The use of the cemented lens in the fourth lens group may be advantageous to correction of chromatic aberrations, but it is difficult to correct especially an inclination of an image plane in an excellent manner.
Therefore, the applicant of Japanese Patent Application No. 2010-127440, the priority of which is claimed in this patent application, proposed 5-group zoom lenses for projection in Japanese Unexamined Patent Publication No. 2009-69539 (Patent Document 4) and Japanese Unexamined Patent Publication No. 2009-69540 (Patent Document 5). In Patent Documents 4 and 5, such an inclination of an image plane is corrected in an excellent manner by providing an air lens that functions as a negative lens in a fourth lens group, which is the fourth lens group from the magnification side of the zoom lens.
However, in the zoom lenses for projection disclosed in Patent Documents 4 and 5, a request for more excellent correction of various aberrations increased. Especially, more excellent correction of both spherical aberrations and coma aberrations was requested.